The Mediterranean and Middle East theatre, also known as the Mediterranean Theater of War, was a major theatre of operations during the Second World War. The vast size of the theatre saw interconnected land, naval, and air campaigns fought for control of the Mediterranean Sea, North Africa, the Horn of Africa, the Middle East and Southern Europe. Despite their disparate geographic locations and objectives, these operations were not seen as neatly separated from each other, but part of an extensive, contiguous theatre of war.

The Mediterranean theater had the longest duration of the Second World War. Combat started on 10 June 1940 with Italy's declaration of war against the United Kingdom and France and ended on 2 May 1945 when all Axis forces in Italy surrendered. In Germany military history, the scope of the theatre is described as Mediterranean, South-East Europe, and North Africa 1939–1941. Additionally, various post-war conflicts, such as the Greek Civil War and the first phase of the Palestine War, were rooted in events during the Mediterranean theater.

The Mediterranean theatre was initially driven by Italian aspirations to establish a new Roman Empire, while the Allies aimed to retain the status quo. Immediately following its declaration of war, Italy invaded France, bombed Malta, and engaged Allied ships. Italian forces invaded Greece in October 1940, requiring German intervention to conquer it by April 1941; Yugoslavia was invaded and occupied by Axis forces the same month. Allied and Axis forces fought across North Africa, while Axis interference in the Middle East caused fighting to spread as far as Palestine, Iraq, and Iran.

With confidence high from early gains, German forces planned to capture the Middle East with a view to possibly attacking the Soviet Union from the south. Devastating losses in Egypt and Tunisia stopped the Axis threat in North Africa by May 1943. The Allies then invaded Italy, resulting in an armistice and subsequent civil war. A prolonged battle for Italy commenced between Allied and Axis forces, supported by the Allied-aligned Kingdom of Italy in the south and Axis-aligned Italian Social Republic in the north, lasting until 2 May 1945 with the Surrender at Caserta.

The Mediterranean and Middle East theatre resulted in the destruction of the Italian Empire and the weakening of Germany's strategic position, as German forces had been diverted from the Western and Eastern fronts and suffered over two million losses (including those captured upon final surrender). Italy lost around 177,000 men, with a further several hundred thousand captured throughout the duration of the theatre. British losses amount to over 300,000 men killed, wounded, or captured, while total American losses in the region were around 130,000.

During the late 1920s, Benito Mussolini claimed that Italy needed an outlet for its "surplus population" and that it would be in other countries' best interests to aid in this expansion. The regime wanted "hegemony in the Mediterranean–Danubian–Balkan region" and the gaining of world power by the conquest "of an empire stretching from the Strait of Gibraltar to the Strait of Hormuz". The Fascists had designs on Albania, Dalmatia, large parts of Slovenia, Croatia, Bosnia and Herzegovina, Macedonia and Greece and harked back to the Roman Empire. The regime also sought to establish protectorates with Austria, Hungary, Romania and Bulgaria. Covert motives were for Italy to become the dominant power in the Mediterranean, capable of challenging France or Britain and gaining access to the Atlantic and Indian Oceans.

On 30 November 1938, Mussolini addressed the Fascist Grand Council on the goal of capturing Albania, Tunisia, Corsica, the Ticino canton of Switzerland and "French territory east of the River Var (to include Nice, but not Savoy)". Mussolini alleged that Italy required uncontested access to the oceans and shipping lanes to ensure its national sovereignty. Italy was a "prisoner in the Mediterranean" and had to break the chains of British and French control. Corsica, Cyprus, Gibraltar, Malta, Suez and Tunisia would need to be taken and Egypt, France, Greece, Turkey and the United Kingdom had to be challenged. Through armed conquest, the north and east African colonies would be linked and this 'prison' destroyed. Italy would be able to march "either to the Indian Ocean through the Sudan and Abyssinia, or to the Atlantic by way of French North Africa". On 2 October 1935, the Second Italo–Ethiopian War began when Italian forces invaded Abyssinia.

Mussolini lauded the conquest as a new source of raw materials and location for emigration and speculated that a native army could be raised there to "help conquer the Sudan. "Almost as soon as the Abyssinian campaign ended, Italian intervention in the Spanish Civil War" began. On 7 April 1939, Mussolini began the Italian invasion of Albania and within two days had occupied the country. In May 1939, Italy formally allied to Nazi Germany in the Pact of Steel.